# -*- coding: utf-8 -*-
"""
Created on Wed Jul 26 20:19:03 2017

@author: lilin
"""

import pygame

from pygame.sprite import Sprite

class Alien(Sprite):
    """表示单个外星人的类"""
    
    def __init__(self,ai_settings,screen):
        """初始化外星人并设置其起始位置"""
        super(Alien,self).__init__()
        self.screen=screen
        self.ai_settings=ai_settings
        
        #加载外星人图像，并设置其rect属性
        self.image=pygame.image.load('images/alien.bmp')
        self.rect=self.image.get_rect()
        
        #每个外星人最初都在屏幕左上角附近
        self.rect.x=self.rect.width
        self.rect.y=self.rect.height
        
        #存储外星人的准确位置
        self.x=float(self.rect.x)
        
    def blitme(self):
        """在制定位置绘制外星人"""
        self.screen.blit(self.image,self.rect)
        
    def update(self):
        """向右或左移动外星人"""
        self.x += (self.ai_settings.alien_speed_factor*self.ai_settings.fleet_direction)
        self.rect.x = self.x 
        
    def check_edges(self):
        """如果外星人处于屏幕边缘，就返回True"""
        screen_rect = self.screen.get_rect()
        if self.rect.right >= screen_rect.right:
            return True
        elif self.rect.left<= 0:
            return True
        
        